Vehicle speed control device actuating mechanism

ABSTRACT

An actuating mechanism for initiating the operation of a speed control device which brakes a railroad vehicle should it exceed a predetermined speed. The actuating device consists of a flexible sensor hose containing a liquid subject to the weight of the railroad vehicle to operate and to close a pressure contact in an electrical circuit to energize a ground mounted or railside mounted tripping mechanism in the form of an electromagnet in the railroad classification yard which, in turn, trips the vehiclemounted speed control device on a railroad car passing over the electromagnet for slowing down the speed of the railroad car. The electromagnet will not be energized to the &#39;&#39;&#39;&#39;on&#39;&#39;&#39;&#39; condition until sufficient time has elapsed as determined by a timer in the electrical circuit of the electromagnet and thereby only &#39;&#39;&#39;&#39;standing&#39;&#39;&#39;&#39; cars rather than &#39;&#39;&#39;&#39;passing&#39;&#39;&#39;&#39; cars turn on the electromagnet. A modified form of the device utilizes two such sensor hoses and pressure switches in a common circuit whereby both pressure switches must be closed in order to energize the electromagnet, the spacing distance between the sensor hoses being greater than the distance between the fore and aft railroad car trucks and the length of each of the hoses or sensing units being greater than the distance between the trucks.

United States Patent Peterson 1 51 Dec. 26, 1972 [54] VEHICLE SPEEDCONTROL DEVICE ACTUATING MECHANISM [72] Inventor: William H. Peterson,I-Iomewood,

Ill.

[73] Assignee: Pullman Incorporated, Chicago, Ill.

[22] Filed: Dec. 28, 1970 [2]] Appl. No.: 101,927

52 us. 01. ..l04/26 R, 246/182 B, 246/271 51 161.01 ..B6lb 1/00, B6113/12 58 Field 61 Search ..246/93, 95, 100, 116, 271,

246/182 B, 192, 201, 202, 24s; 104/26 R Primary Examiner-Gerald M.Forlenza Assistant Examiner-George l-l. Libman Attorney-Hilmond O. Vogeland Richard J. Myers [5 7] ABSTRACT An actuating mechanism forinitiating the operation of a speed control device which brakes arailroad vehicle should it exceed a predetermined speed. The actuatingdevice consists of a flexible sensor hose containing a liquid subject tothe weight of the railroad vehicle to operate and to close a pressurecontact in an electrical circuit to energize a ground mounted orrailside mounted tripping mechanism in the form of an electromagnet inthe railroad classification yard which, in turn, trips thevehicle-mounted speed control device on a railroad car passing over theelectromagnet for slowing down the speed of the railroad car. Theelectromagnet will not be energized to the on condition until sufficienttime has elapsed as determined by a timer in the electrical circuit ofthe electromagnet and thereby only standing cars rather than passingcars turn on the electromagnet. A modified form of the device utilizestwo such sensor hoses and pressure switches in a common circuit wherebyboth pressure switches must be closed in order to energize theelectromagnet, the spacing distance between the sensor hoses beinggreater than the distance between the fore and aft railroad car trucksand the length of each of the hoses or sensing units being greater thanthe distance between the trucks.

20 Claims, 7 Drawing Figures PATENTEflnEczs m2 3.707.124

sum 2 or 2 SPEED MAGNETICALLY T 15 RESPONSIVE JQGENERATOR J6RESPONSIVE\SWITCH I SWITCH a SPEED CONTROL L9 ,5 PRIOR ART DEVICE Z 7 RELAY 2$EM isaksa' 74%;, #firsm VEHICLE SPEED CONTROL DEVICE ACTUATING MECHANISMBACKGROUND OF THE INVENTION 1. Field of the Invention The field of artto which this invention pertains is the railroad car art and, inparticular, relates to speed con trol devices for the railroad car,especially for use in the railroad classification yard.

2. Description of the Prior Art It is known in the prior art to providefor various types of speed control devices for regulating the speed of arolling railroad car within a classification yard. It is important,however, to regulate the triggering or tripping devices by switches thatinitiate the operation of the railroad car speed control device suchthat these tripping devices will not operate until their operation isrequired. It is for this particular problem the invention finds thesolution.

SUMMARY It isa'general object and purpose of this invention to providefor an actuating mechanism for operating carmounted speed controldevices at various'points along the railroad track as, for instance, ina classification yard. More particularly, it is an object of thisinvention to provide for means for sensing the presence of a standingrailroad car and then to energize groundmounted speed control devicetripping mechanisms and to actuate the speed control device on therailroad car to limit the free rolling speed of the railroad car withinthe classification yard. The operation of such a speed control devicehas been previously described in U.S. Pat. No. 3,524,982 to William H.Peterson.

Another object of this invention is to provide for a sensor device whichsenses the presence of the standing railroad car and then operates apressure switch'and timed relay device to operate an electromagnetmounted on the railroad car ladder track in a classification yard wheresuch electromagnet is a considerable distance further removed upstreamor uphill from the location of the standing car. The invention providesfor sequential energization of these speed control device triggeringelectromagnets that are spaced further and further away upstream fromthe location where the first or initial standing cars came to rest. As aseries of cars are formed into a train, as a particular car contacts asensing arrangement, track-mounted electromagnets closer upstream towardthe entrance of the ladder track in the classification yard areactivated to control the speed of the railroad car at an earlier timeduring its entrance into the ladder track.

These and other objects of the invention will become more apparent byreference to the following description, appended claims and attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view of aclassification yard showing a series of tracks with a system of railroadcar speed control device actuating mechanisms;

FIG. 2 is a view schematically showing a section of railroad track in aclassification yard wherein there is provided the electromagnetactuating mechanism for operating a vehicle speed control device and thesensor unit or hose and pressure contact switch and timer to operate theelectromagnet;

FIG. 3 is a sectional view illustrating the relation between therailroad car wheel and the sensor unit or flexible hose;

FIG. 4 schematically discloses the pressure-responsive switcharrangement of the actuating mechanism for the vehicle speed controldevice;

FIG. 5 is a schematic view of the electrical circuit including theelectromagnet, the pressure switch and the timer;

FIG. 6 is'a schematic view of a railroad car speed control device of thetype shown in U.S. Pat. No. 3,524,982; and

FIG. 7 is a modified arrangement of the actuating arrangement forinitiating the operation of the railroad car speed control device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIGS. 1-6and in particular with reference to FIG. 1, there is shown aclassification yard 1 provided with a plurality of ladder tracks 2. Eachladder track 2 has a railroad car entrant or beginning portion 3 andmain portion 4 following the entrant or upstream portion 3. Inoperation, a railroad car, such as shown in dotted line at 5, moves fromthe entrant portion along the track 2 and into the central area portion4 to couple with a standing car 6 at the other end or downstream ordownhill of the central portion 4 of the track 2. The ladder track 2 hasa slight downhill grade to permit the railroad car 5 to roll along itand couple with the standing car 6 to form part of a train, as is theusual practice. Should the car 5 be traveling too fast, a speed controldevice 7 mounted on the car passes by the track-mounted magnet 8 and isactuated to apply the vehicle air brakes as, for instance, shown by U.S.Pat. No. 3,524,982 to W. H. Peterson, and incorporated herein byreference thereto. Consequently, the car 5 is slowed down to a desirablespeed, say, between 3 and 4 m.p.h. and coupled with car 6 and overliesthe novel inventive vehicle speed control device actuating mechanism 9which, when tripped by the presence of the vehicle, operates itselectromagnet unit 10 which will actuate the speed control device of thenext car coming down the ladder track 2 to brake the vehicle as itpasses over the electromagnet 10. Thus the next successive uphill carsare braked earlier in place and time by the electromagnet unit 10. Aftera number of cars have been coupled, eventually the last car of thatgroup will be over another actuating mechanism 9 that is just to theright of the permanent magnet unit 8. This vehicle actuating mechanism 9will then be activated by the standing car over it to operate itsassociated electromagnet unit 10 which is closest to the entrant portion3 of the track 2 so that subsequent cars entering the track area willimmediately have their speed control device activated by the entrantelectromagnet unit 10 of the actuating mechanism 9 located closest tothe entrant portion 3 of the track 2. The other ladder tracks 2 shown inFIG. 1 similarly contain a plurality of vehicle speed control deviceactuating mechanisms 9 provided with electromagnets 10 spaced up-tracktherefrom and connected by electrical wire means 11. By such anarrangement it is seen that as the left end of the ladder tracks fill upfrom left to 7 right (FIG. 1) with cars progressively the actuatingmechanisms from left to right become activated because of the presenceof a standing car thereat.

In FIGS. 2-5 there is shown a first embodiment which comprises aparticular actuating mechanism 9 which includes a electromagnet 10, asensor 18, a trigger or pressure-responsive switch 20, power source orbattery 21, and time delay relay 23, and how a car 5 effects theoperation of the actuating mechanism 9 which, in turn, has itselectromagnet unit 10 trigger the speed control device 7 on the vehicle5 to brake the speed of the vehicle as disclosed in the aforementionedpatent. The speed control device 7, (see FIG. 6) as disclosed by thesaid patent includes a brake system 12 which is operated by air pressurefunneled by the solenoid valve 13 when the ladder is energized bytherailroad car driven generator 14 when the centrifugal orspeed-responsive switch 15 is closed when the vehicle exceedsapproximately 4 mph and the magnetically responsive switch 16 has beenacted upon by the permanent magnet 8 or an energized electromagnet 10 tooperate relay l7 attendant to energizing the solenoid 13. When thevehiclespeed falls below the speed of 4 m.p.h., the centrifugal switch15 opens the circuit and de-energ izes the holding relay l7de-energizing the solenoid valve and preventing further application ofair brake pressure to the vehicle brake system.

The components of an actuating mechanism 9 are shown in FIG. 2 andinclude the compressible or flexible member or hose 18 which acts as asensor which senses the presence of the railroad car in that it containsenclosed within it a fluid such as a liquid 19 which acts on thepressure-responsive switch means 20 to close the circuit to the powersource or electric battery 21 and the electromagnet means 10. Thepressureresponsive switch means 20 is responsive to the sensor 18 andtriggers or energizes the circuit 22 containing the battery 21, theelectrom agnet 10 and the time delay relay means 23. In FIG. 3 it isseen that the railroad wheel 24 of the car 5 has its outer portion 25compressing the flexible hose 18 while the main body portion 26 of therailroad wheel 24 rests on the upper part 27 of the rail 28 while theupright flange portion 29 of the rail 28 carries a Z-shaped bracket 30by bolt means 31 which supports lengthwise of the track the hose orsensor 18. The outer end 18a of the hose 18 is closed and the inner end18b of the hose is open (see FIGS. 2 and 4) and exposed to the flexiblediaphragm 20a of the pressure-responsive switch means 20 which alsoincludes a housing 20b and a micro-switch or contact button 20c whichmoves contact 20d into engagement with contact arm 20c for closing thecircuit 22 at the place where the pressure-responsive switch 20 islocated, the contact arms 20:: and 20d being mounted in the housing 32which also contains the time delay relay means 23.

The time delay relay mechanism 23 is best seen in FIG. 5 and includesthe relay unit 33, the potentiometer or a variable resistance controlmeans 34, motor means 35, cam means 36, first timer contact means 37 andsecond timer contact means 38. The polarity or direction of current flowof circuit 22 in FIG. 5 is shown as positive with a plus sign and asnegative with a minus sign and electrical ground is designated by theletter G.

When the pressure responsive switch means 20 is closed, the relay coil33a of relay 33 is energized and moves its contact members 33b and 330from the solid line position of engagement with contacts 39 and 40respectively to the dotted line position of engagement with contacts 41and 42 to operate motor means 35 causing rotation of motor means and cammeans 36 in a clockwise direction. Such movement of the relay contactarms 33b and 33c also places the variable resistance means 34, whichpermits adjustment of the length of time of operation of the delay means23, in the circuit. The variable resistance means 34 is set at a desiredposition to control the current flow where a smaller amount of currentis sent to the motor means to rotate it more slowly in the clockwisedirection than in the counter-clockwise direction when the resistancemeans 34 is not in the circuit. As cam means 36 rotates clockwise, thebufl'er portion 370 of the spring contact member 37b rides out of camslot 36a to move contact member 37b against spring contact member 370 toclose the circuit between line portions 43 and 44. Contact members 37bvand 370 function to later terminate reverse rotation of the motor means35 during subsequent rotation. When cam slot 36a rotates from thatposition shown in FIG. 5, the buffer 38a of spring contact member 38b ofcontact means 38 enters the slot 36a (because the spring element 38b isbiased towards the cam means 36) and spring contact element 380 which isalso biased toward cam means 36 engages and closes with contact element38d, the electromagnet 10 is energized. As this happens, previouslyclosed contacts 38c and 38f of members 380 and 38b, respectively,separate and open the circuit to motor means 35 and stop clockwiserotation of the motor means 35. As the completed train is pulled out ofthe classification yard carrying the car 5 away from the sensor 18, thepressure switch means 20 opens the circuit causing the relay 33 torelease with contacts 33b and 330 going to the solid line positionillustrated which reverses polarity of the motor means 35, therebycausing motor to move in a counter-clockwise direction. Since resistancemeans 34 is now out of the circuit which is operating the motor means,motor means 35 causes a rapid or fast movement of the cam slot 36a awayfrom buffer 38a to de-energize the electromagnet 10 by opening theengaged contact members 38c, 38d and for fast return of the cam slot 36ato engage with the buffer 37a and opens contacts 37b and 370 to stopmotor means 35. Similarly, any time the car leaves the sensor before theelectromagnet 10 is energized by the buffer 38a entering the slot 37a,i.e. when cam means 36 rotates less than 180 or, say, approximately twoor three minutes to indicate a car is merely temporarily over or passingover the sensor 18, as distinguished from being a standing or stoppedcar on the sensor 18, the motor polarity is reversed to cause a rapidreverse rotation of the cam means to place the cam slot 36a inengagement with the buffer 37a. The length of a particular hose orstanding railroad car sensor unit 18 should be greater than the distancebetween the railroad car trucks of the largest railroad car in theclassification yard.

In the modification shown in FIG. 7, there is shown two such sensorunits 18' and 18" connecting with pressure-responsive switches 20' and20" respectively. The switches 20' and 20" are in a common circuit 45and are connected to one another by a common electrical line 46. Thereis a battery 21 adjacent each pressure switch 20' or 20", their polaritybeing the same so that their output is additive. It will be appreciatedthat only one battery would be effective to operate the circuit 45. Thecircuit 45 also is provided with a groundmounted or railside mountedtripping mechanism or electromagnet 101. By this arrangement, not onlyis the length of the sensor hoses 18' and 18" greater than the distancebetween the trucks at each end of the car or between the fore and aftpair of car trucks but the spacing distance between each of the sensors20' and 20" is greater than the distance between said fore and aftrailroad car trucks. If the distance between the sensors and the lengthof the sensors exceeded the length of the longest railroad car, this, ofcourse, would provide for an adequate sensing arrangement in theactuating mechanism 9. The actuating mechanism 9' of the modified formshown in FIG. 7 requires that two railroad cars must be coupled togetherand standing over the respective sensor units 18 and 18" before theassociated electromagnet 10' is energized. The distance between thesensor 18" and the electromagnet 10 should be not less than three orfour railroad car lengths in order to give the braked railroad carsufficient stopping distance but actually it would be preferable to havethe electromagnet spaced considerably more up toward the entrant portionof the ladder track and could also be true in the case of the firstembodiment shown in FIGS. 1-5. One preferred arrangement in theclassification yard would be to use one perv manent magnet or anelectromagnet for braking the speeds of the free rolling cars half-waydown (or more) of a particular ladder track and then to have the sensorof the first embodiment or the sensors of the second embodiment locatedjust adjacent the permanent magnet and between the permanent magnet andthe entrance of the ladder track and then to have an electromagnet thatis to be energized by a particular sensor or sensors be located at theentrance of the ladder track. As a train builds up to where carsare'standing anywhere along the length of the hose of the first embodiment or a pair of hoses of the second embodiment, then theelectromagnet will activate the car-mounted speed control device as thecars enter the ladder track. In the first mentioned embodiment only acar standing anywhere along the length of the sensor or hose closes thepressure switch which energizes the time delay relay and if the pressureswitch remains closed for longer, say, than three minutes, then thecontacts in the time delay relay close, completing the circuit andenergizing the electromagnet at the head end of the ladder track.

The foregoing description and drawings merely explain and illustrate theinvention and the invention is not limited thereto, except insofar asthe appended claims are so limited, as those skilled in the art who havethe disclosure before them will be able to make modifications andvariations therein without departing from the scope of the invention.

What is claimed is:

l. A ground-mounted actuating mechanism for a vehicle-mounted speedcontrol device comprising:

sensor means in the path of a first vehicle sensing thepresence of thefirst vehicle in a first location,

triggering means in said path and spaced upstream from said firstlocation at a second location for operation the vehicle-mounted speedcontrol device of a second vehicle passing said second location,

power means connected with said triggering means and said sensor means,

sensor switch means connected with said sensor means, said power meansand said triggering means and responsive to said sensor means toenergize said triggering means after a time delay greater than thenormal time for a moving vehicle to pass said sensor means, wherebyswitching will occur only when a vehicle is standing at said sensormeans.

2. The invention according to claim 1, and

the length of said sensor means being at least the extent of thedistance between the fore and aft wheelsof the vehicle.

3. The invention according to claim I, and

a second triggering means spaced downstream from said first mentionedtriggering means for actuating the speed control device on said firstvehicle prior to the energizing of said first mentioned triggering meansby said sensor means sensing the first vehicle in the first location.

4. The invention according to claim 3, and

said second triggering means spaced downstream from said firsttriggering means in a third location.

5. The invention according to claim 1, and

said sensor means including a flexible tube having a fluid therein andsaid sensor switch means including a pressure-responsive switchresponsive to the pressure on the tube exerted by the presence of thefirst vehicle.

6. The invention according to claim 1, and

said sensor means including a compressible member and said sensor switchmeans including a switch member responsive to the compression of saidcompressible member by the presence of the first vehicle.

7. The invention according to claim 1, and

time delay relay means connected with said sensor switch means and uponactuation of the sensor switch means by the sensor means being operativeto measure a predetermined duration of the presence of the first vehicleat the first location attendant to energizing of the triggering means atthe termination of said duration.

8. The invention according to claim 7, and

said time delay relay means including means for resetting said timedelay relay means should said sensor means de-activate said sensorswitch means prior to the first vehicle leaving the first locationbefore completion of the predetermined duration.

9. The invention according to claim 1, and

said sensor means including a pressure-responsive tube means containinga fluid and said sensor switch means including a pressure-responsiveswitch operative to a closed position by the pressure of said fluidthereon when the first vehicle exerts a force on the sensor means.

10. The invention according to claim 9, and

said triggering means including an electromagnet energized by theclosing of said pressure-responsive switch.

1 1. The invention according to claim 10, and

said power means including a battery for supplying electricity toenergize said electromagnet.

12. The invention according to claim 3, and

said second triggering means including a permanent magnet and operativeon the speed control device of said first vehicle attendant to brakingthe speed of said first vehicle.

13. A ground-mounted actuating mechanism for vehicle-mounted speedcontrol devices;

each vehicle mounted speed control device including amagnetically-responsive switch triggered by said ground-mountedactuating mechanism for applying the associated vehicle brakes attendantto slowing down the vehicle speed,

said ground-mounted actuating mechanism including sensor means in thepath of a first vehicle for sensing the presence of the first vehicle ina first location, 1

triggering means in the form of an electromagnet in said path and spacedupstream from said first location at a second location for operating thevehiclemounted speed control device of a second vehicle passing saidsecond location,

a source of electrical power connected to said electromagnet and saidsensor means, and

sensor switch means connected with said sensor means, said source ofelectrical power and said electromagnet and acted upon by said sensormeans to energize the electromagnet when said first vehicle stands atthe first location a predetermined time greater than the normal time fora moving vehicle to pass said sensor means, whereby when the secondvehicle passes by the energized electromagnet the speed control deviceof the second vehicle is energized by the electromagnet to brake thespeed of the second vehicle.

14. The invention according to claim 13, and

said switch means including a time delay relay means for determiningsaid predetermined time.

15. The invention according to claim 13, and

a second magnet located downstream of said electromagnet to activate thespeed control device on said first vehicle.

16. In a railroad classification yard, an arrangement for controllingthe speed of free rolling railroad cars on a downwardly sloping railroadtrack wherein the cars are provided with speed control devices activatedfor car braking in excess of a predetermined car speed,

a trackside electromagnet located uphill toward the entrance of thetrack and adapted when energized to activate a speed control device on afirst railroad car at a first location near the electromagnet,

a railroad car sensor located at trackside and downhill from theelectromagnet and adapted to sense the presence of a second railroad carlocated at a second location proximate the sensor,

a time delayed sensor switch and a power source associated with thesensor and the electromagnet in a common circuit whereby the firstrailroad car located at the sensor for a time'greater than the delaytime energizes the electromagnet which activates subsequent speedcontrol devices on cars passing by said electromagnet whereby only carsat rest at said sensor will cause actuation of said sensor switch.

17. The invention according to claim 16, and

a magnet member at trackside downhill from the electromagnet foractivating the speed control d ic ofac r ass hereb. 18. i iie inventiemacc r ing to c laim l7, and

said magnet member being between the sensor and the electromagnet.

19. The invention according to claim 16, and

said sensor switch including a timer means determining the duration ofthe presence of the second railroad car at the second location attendantto energizing the electromagnet at the termination of said duration.

20. The invention according to claim 16, and

said sensor comprising a pressure-responsive fluid bearing tube and saidswitch comprising a pressure-responsive member and a switch memberclosed thereby with closing of the circuit before the power source andthe electromagnet.

1. A ground-mounted actuating mechanism for a vehicle-mounted speedcontrol device comprising: sensor means in the path of a first vehiclesensing the presence of the first vehicle in a first location,triggering means in said path and spaced upstream from said firstlocation at a second location for operation the vehiclemounted speedcontrol device of a second vehicle passing said second location, powermeans connected with said triggering means and said sensor means, sensorswitch means connected with said sensor means, said power means and saidtriggering means and responsive to said sensor means to energize saidtriggering means after a time delay greater than the normal time for amoving vehicle to pass said sensor means, whereby switching will occuronly when a vehicle is standing at said sensor means.
 2. The inventionaccording to claim 1, and the length of said sensor means being at leastthe extent of the distance between the fore and aft wheels of thevehicle.
 3. The invention according to claim 1, and a second triggeringmeans spaced downstream from said first mentioned triggering means foractuating the speed control device on said first vehicle prior to theenergizing of said first mentioned triggering means by said sensor meanssensing the first vehicle in the first location.
 4. The inventionaccording to claim 3, and said second triggering means spaced downstreamfrom said first triggering means in a third location.
 5. The inventionaccording to claim 1, and said sensor means including a flexible tubehaving a fluid therein and said sensor switch means including apressure-responsive switch responsive to the pressure on the tubeexerted by the presence of the first vehicle.
 6. The invention accordingto claim 1, and said sensor means including a compressible member andsaid sensor switch means including a switch member responsive to thecompression of said compressible member by the presence of the firstvehicle.
 7. The invention according to claim 1, and time delay relaymeans connected with said sensor switch means and upon actuation of thesensor switch means by the sensor means being operative to measure apredetermined duration of the presence of the first vehicle at the firstlocation attendant to energizing of the triggering means at thetermination of said duration.
 8. The invention according to claim 7, andsaid time delay relay means including means for resetting said timedelay relay means should said sensor means de-activate said sensorswitch means prior to the first vehicle leaving the first locationbefore completion of the predetermined duration.
 9. The inventionaccording to claim 1, and said sensor means including apressure-responsive tube means containing a fluid and said sensor switchmeans including a pressure-responsive switch operative to a closedposition by the pressure of said fluid thereon when the first vehicleexerts a force on the sensor means.
 10. The invention according to claim9, and said triggering means including an electromagnet energized by theclosing of said pressure-responsive switch.
 11. The invention accordingto claim 10, and said power means including a battery for supplyingelectricity to energize said electromagnet.
 12. The invention accordingto claim 3, and said second triggering means including a permanentmagnet and operative on the speed control device of said first vehicleattendant to braking the speed of said first vehicle.
 13. Aground-mounted actuating mechanism for vehicle-mounted speed controldevices; each vehicle mounted speed control device including amagnetically-responsive switch triggered by said ground-mountedactuating mechanism for applying the associated vehicle brakes attendantto slowing down the vehicle speed, said ground-mounted actuatingmechanism including sensor means in the path of a first vehicle forsensing the presence of the first vehicle in a first location,triggering means in the form of an electromagnet in said path and spacedupstream from said first location at a second location for operating thevehicle-mounted speed control device of a second vehicle passing saidsecond location, a source of electrical power connected to saidelectromagnet and said sensor means, and sensor switch means connectedwith said sensor means, said source of electrical power and saidelectromagnet and acted upon by said sensor means to energize theelectromagnet when said first vehicle stands at the first location apredetermined time greater than the normal time for a moving vehicle topass said sensor means, whereby when the second vehicle passes by theenergized electromagnet the speed control device of the second vehicleis energized by the electromagnet to brake the speed of the secondvehicle.
 14. The invention according to claim 13, and said switch meansincluding a time delay relay means for determining said predeterminedtime.
 15. The invention according to claim 13, and a second magnetlocated downstream of said electromagnet to activate the speed controldevice on said first vehicle.
 16. In a railroad classification yard, anarrangement for controlling the speed of free rolling railroad cars on adownwardly sloping railroad track wherein the cars are provided withspeed control devices activated for car braking in excess of apredetermined car speed, a trackside electromagnet located uphill towardthe entrance of the track and adapted when energized to activate a speedcontrol device on a first railroad car at a first location near theelectromagnet, a railroad car sensor located at trackside and downhillfrom the electromagnet and adapted to sense the presence of a secondrailroad car located at a second location proximate the sensor, a timedelayed sensor switch and a power source associated with the sensor andthe electromagnet in a common circuit whereby the first railroad carlocated at the sensor for a time greater than the delay time energizesthe electromagnet which activates subsequent speed control devices oncars passing by said electromagnet whereby only cars at rest at saidsensor will cause actuation of said sensor switch.
 17. The inventionaccording to claim 16, and a magnet member at trackside downhill fromthe electromagnet for activating the speed control device of a carpassing thereby.
 18. The invention according to claim 17, and saidmagnet member being between the sensor and the electromagnet.
 19. Theinvention according to claim 16, and said sensor switch including atimer means determining the duration of the presence of the secondrailroad car at the second location attendant to energizing theelectromagnet at the termination of said duration.
 20. The inventionaccording to claim 16, and said sensor comprising a pressure-responsivefluid bearing tube and said switch comprising a pressure-responsivemember and a switch member closed thereby with closing of the circuitbefore the power source and the electromagnet.